In a typical wireless cellular network, an active mobile is registered to a cell, termed the serving cell. When the signal quality received by the mobile from the serving cell is insufficient, the mobile must find another cell to be used as the new serving cell. This procedure of selecting a new serving cell is called handover, and the cell selected as the new serving cell is called the handover target cell. In one network, for example, the current serving cell broadcasts a list of neighboring cells that are potential candidates for selection as the handover target cell. This list is referred to as the neighbor cell list.
To find a suitable target cell, the mobile scans cells included in the neighbor cell list. The neighbor cell list must include enough potential candidates so that even where the position of the mobile is uncertain or the current state of neighboring cells is unknown, it is likely that the mobile will be able to find a target cell with a sufficiently powerful signal or good enough signal-to interference ratio (SINR) to enable to mobile to successfully handover to a target cell and attach to it. The serving cell allocates time intervals during which the mobile may perform the scanning procedure. The time duration during which the mobile performs scanning is divided into interleaving intervals: time periods for normal transmission (called listening intervals); and time periods for scanning (called scanning intervals).
Some types of wireless network currently being developed aim to provide broadband access mobile networks, such as those in accordance with IEEE 802 standards, also sometimes referred to as WiMAX. In one WiMAX network, as schematically shown in FIG. 1, a serving base station 1 serving a mobile 2 sends a message MOB_NBR-ADV to the mobile 2 at intervals. This message includes a neighbour cell list. At a time t1, the mobile 2 determines that handover may be required, for example, if the quality of the signal it is receiving from its serving cell drops below a threshold quality level. The mobile 2 sends a message MOB_SCN-REQ to the base station 1 indicating that it needs to perform scanning. The base station 1 sends a message MOB_SCN-RSP giving time periods allocated to the mobile 2 as scanning intervals. The mobile 2 then scans the cells in the neighbour cell list at the times defined as scanning intervals. During scanning, there is no communication of payload data between the mobile 2 and its serving cell. Thus throughput of data is reduced compared to periods when no scanning is required.